1. Field of the Invention
This invention relates to photographic silver halide emulsions, and to organic compounds which increase their sensitivity without an adverse effect on fog.
2. State of the Art
Organic compounds which contain sulfur and nitrogen are widely used within the photographic art. Plakunov and Koller in U.S. Pat. No. 3,708,302 disclosed that the reaction product of cysteine and glutaraldehyde (GDA) could be employed in a layer on the same side of the support as a silver halide emulsion layer in order to improve sensitivity without adversely affecting fog. Amering in U.S. Pat. No. 3,869,289 later disclosed that the same reaction product could be employed in a photographic developer composition to increase speed. Both references teach that one should avoid having the silver halide emulsion come into intimate contact with said reaction product prior to development.
Scavron, U.S. Pat. No. 3,565,625 and Spath, U.S. Pat. No. 2,860,976 relate to the use of thiazolidines within photographic films and developers respectively, with a particularly useful moiety being thiazolidine-4-carboxylic acid (TCA). These and other references illustrate that heterocyclic compounds containing nitrogen and sulfur can be employed for a variety of purposes such as sensitization, stabilization, development and dye-formation. Therefore, a high degree of skill would be required to associate specific photographic characteristics with any particular chemical structure. While it was known that the reaction of cysteine with glutaraldehyde or a chemical equivalent thereof produced a product which could enhance the sensitivity of a silver halide film, a disadvantage connected with this technique was fog formation which was often variable. There is no disclosure in the art of how to obtain the enhanced sensitivity without increasing fog. The present invention provides that disclosure.